The present invention relates to a method and an apparatus which determine a sequence that parts are mounted on a printed circuit board and the like by a turret table mounter having a plurality of heads. More particularly, the present invention relates to a method and an apparatus which determines the mounting sequence in a parts mounting system comprising a turret table mounter, a part feeder which feeds a part from a plurality of kinds of part cassettes to the turret table mounter, and a positioner which positions the circuit board.
The present application relates to the method and apparatus which determines the mounting sequence in the system utilizing the "mounting system" of the application U.S. Ser. No. 07/552,126 which is the co-assigned application of the present application. Therefore, the co-assigned application is incorporated into the present application by reference.
As a conventional apparatus, a turret table mounter has been used to mount small electric parts on a printed circuit board. The turret table mounter comprises a turret table having a plurality of heads which perform a rotary operation. In the mounting operation of the turret mounting apparatus, one of the heads normally picks up a part at a single fixed point (which is referred to as a "pickup position" thereafter), and the turret is rotated 180 degree, and then the head holding the part inserts the part to the printed circuit board at the position located 180 degree from the pickup position (which is referred to as an "insertion position" thereafter).
In this way, in the turret table mounter, the following operations are necessary: the head picks up a part, the head holding the part is moved to the insertion position, and the part is inserted into the printed circuit board. A head can hold only parts which fit to the shape of the head. Therefore, the head which cannot pick up the part locating at the pickup position must rotate without picking up any part. Thus, in what sequence the part is picked up or inserted considerably affects the time required for parts mounting.
The part feeder which feeds a part to the turret table mounter usually comprises a cassette moving mechanism having a plurality of part cassettes which moves the cassette with the necessary parts to the pickup position. Therefore, in what sequence the part feeder feeds parts affects the time required for adjusting a mounting position, that is, the efficiency of parts mounting.
Furthermore, on the printed circuit board, mounting positions (normally "lead holes" are provided on a mounting position) to which a plurality of parts (e.g. IC packages or tip resistors) are inserted can be set in advance. With such a setting, the positioner moves and positions the board so that each mounting position reaches the insertion position. Since the arrangement of parts to be mounted is two-dimensional on the printed circuit board, the sequence of the parts mounting considerably affects the time required for mounting.
Thus, in a mounting system utilizing a turret table mounter, the appropriate sequence for parts mounting needs to be determined because the sequence of parts mounting considerably the efficiency of mounting.
In the conventional arts, the "single-point searching method" or "whole-point searching method" is utilized as a method to determine the sequence of parts mounting.
The "single-point searching method" is a method which determines a part which is the closest to the part which has been determined in step n-1 as the part to be mounted in step n. The "whole-point searching method" is a method which searches all groups of the sequences on the all parts to be mounted and examines the sequence of each part of the group.
In the conventional arts, there are the following drawbacks In the "single-point searching method", as the number of parts to be mounted increases, the accuracy of resolution decreases, while in the "whole-point searching method", the time required for calculation increases and becomes beyond practical use.
Furthermore, in the conventional mounting system, there is another drawback. Normally, a single turret table mounter is required to mount parts on at least two kinds of printed circuit boards. But in the conventional method in order to determine the sequence of parts mounting, the sequence is usually determined by taking into consideration the arrangement of the part mounting head on the turret and the cassettes in the part feeder for only a Single printed circuit board. The other printed circuit board is not considered at all. Therefore, in the case where at least two kinds of printed circuit boards are to be mounted with parts, the system needs to be stopped to change the arrangement of the heads and/or change some of the heads whenever the kind of a printed circuit board is changed.
Thus, there is the drawback that the production efficiency is decreased because of the time required for adjustment in the turret portion changes in the mounter, as well as the head arrangement for head changes.